Low-current-density LED-pumped Nd: YAG laser using a solid cylindrical reflector

Results of a development program for light-emitting-diode (LED)-pumped neodymium-doped yttrium aluminum garnet (Nd: YAG) lasers highlight a significant design feature: an index-matching method to increase the coupling efficiency of the laser. A solid-glass half-cylinder measuring 5.0×5.6 cm was used for index matching and also as a pumping cavity reflector. An array of twenty 0.034×0.254-cm GaAlAs diodes, connected in series, aligned such that the emission area formed a straight line, was used to excite a 1.5×56-mm laser rod. The interfaces between the diode array, glass half-cylinder, and laser rod were filled with viscous fluid of refractive index n = 1.55. Experiments performed with both the glass half-cylinder and a gold-coated stainless steel reflector under the same operating conditions indicated that the index-matching half-cylinder gave 160–200% improvement of coupling efficiency over the metal reflector at various operating temperatures. For a 207-A/cm2 driving current density the laser produced cw output power of 27 mW.